Retaining mechanism

ABSTRACT

A retaining mechanism for use in affixing a stratum to bone is disclosed. The mechanism comprises a stratum comprising a first surface, a second surface, and a hole extending between the two surfaces. The hole has a central longitudinal axis extending substantially perpendicular to the two surfaces. The retaining element comprises a first position that permits a fastener to be passed through the hole, a second position that at least partially overlaps the hole, and a spring element. The spring element is configured to engage the stratum, configured to move in a direction substantially perpendicular to the central longitudinal axis of the hole when the retaining element moves between its first and second positions, and configured to engage the retaining element to help maintain the retaining element in its second position to help prevent inadvertent backing out of the fastener after it has been fully inserted into the hole.

The present application is a continuation application of U.S. patentapplication Ser. No. 13/600,736, filed Aug. 31, 2012, which is relatedto commonly-owned U.S. patent application Ser. No. 12/970,130, filedDec. 16, 2010, and entitled “Retaining Mechanism,” which is now U.S.Pat. No. 8,454,667. The complete disclosure of each of U.S. patentapplication Ser. No. 13/600,736 and U.S. patent application Ser. No.12/970,130 is incorporated herein by reference, in their entireties.

FIELD OF INVENTION

The present invention is directed to systems for affixing a stratum tobone.

BACKGROUND

The present disclosure relates to retaining mechanisms, and moreparticularly, systems for affixing a stratum to bone.

SUMMARY OF THE INVENTION

A retaining mechanism for use in affixing a stratum to bone isdisclosed. The mechanism comprises a stratum comprising a first surface,a second surface, and a hole extending between the first surface and thesecond surface. The hole has a central longitudinal axis that extendssubstantially perpendicular to the first surface and the second surface,wherein the first surface is configured to engage at least a portion ofthe bone. The retaining element comprises a first position that permitsa fastener to be passed through the hole, a second position that atleast partially overlaps the hole, and a spring element. The springelement is configured to engage the stratum, configured to move in adirection substantially perpendicular to the central longitudinal axisof the hole when the retaining element moves between its first andsecond positions, and configured to engage the retaining element suchthat the spring element helps maintain the retaining element in itssecond position so as to help prevent inadvertent backing out of thefastener after the fastener has been fully inserted into the hole.

Further, a system for affixing stratum to bone is disclosed. The systemcomprises a retaining mechanism and at least one fastener configured topass through the hole in the stratum and engage the bone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric top view of a retaining mechanism for affixing astratum to bone;

FIG. 2 is a cut-away, exploded, isometric top view of retainingmechanism of FIG. 1;

FIG. 3 is a cut-away, isometric top view of the retaining mechanism ofFIG. 1;

FIG. 4 is a cut-away, isometric bottom view of the retaining mechanismof FIG. 1;

FIG. 5 is an isometric top view of the retaining element of FIG. 1;

FIG. 5A is an isometric bottom view of the retaining element of FIG. 1;

FIG. 6 is a cut-away, isometric top view of the stratum of FIG. 1;

FIG. 7 is a cut-away, isometric top view of the retaining mechanism ofFIG. 1;

FIG. 8 is another cut-away, isometric top view of the retainingmechanism of FIG. 1;

FIG. 9 is an isometric top view of another embodiment of a retainingmechanism for affixing a stratum to bone;

FIG. 10 is a top view of the retaining element of FIG. 9;

FIG. 11 is another top view of the retaining mechanism of FIG. 9;

FIG. 12 is a top view of a spring element;

FIG. 12A is a side view of a spring element;

FIG. 13 is a top view of another embodiment of a retaining mechanism foraffixing a stratum to bone; and

FIG. 14 is a top view of the retaining element to be used with theretaining mechanism of FIG. 13.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments, or examples,illustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended. Any alterations andfurther modifications in the described embodiments, and any furtherapplications of the principles of the invention as described herein arecontemplated as would normally occur to one skilled in the art to whichthe invention relates.

FIG. 1 shows an isometric top view of a retaining mechanism 200 foraffixing a stratum 120 to bone, for example, to two or more levels ofvertebral bodies. As shown in FIG. 1, the stratum 120 is designed forconnecting three vertebral bodies (not shown), each vertebral bodyreceiving two fasteners, one fastener through each hole, for example,holes 122 and 122A. As shown in FIG. 1, the stratum 120 may be, forexample, a spinal plate for connecting cervical vertebrae by affixingthe stratum 120 to the anterior surface of the vertebrae. Further, asshown in the Figures and as described herein, the fasteners may be, forexample, screws.

The retaining mechanism 200 comprises a stratum 120, a retaining element160 and a spring element 130. The stratum 120 comprises a first surface119, a second surface 121, and six holes (for example, holes 122 and122A) extending between the first surface 119 and the second surface121. As shown in FIG. 1, the first surface 119 is configured to engageat least a portion of the bone. The retaining element 160 comprises afirst position that permits a fastener to be passed through the hole(for example, hole 122 or 122A), a second position that at leastpartially overlaps the hole (for example, hole 122 or 122A), and aspring element 130 configured to engage the stratum 120 and configuredto engage the retaining element 160 such that the spring element 130helps maintain the retaining element 160 in its second position so as tohelp prevent inadvertent backing out of the fastener after the fastenerhas been fully inserted into the hole (for example, hole 122 or 122A).Note that, as shown in FIG. 1, the stratum contains three retainingmechanisms. One is retaining mechanism 200 and the other two aresimilar, with each mechanism configured for another bone or bonesegment, for example, configured for separate vertebral bodies. Further,note that hole 122 has a central longitudinal axis that extendssubstantially perpendicular to the first and second surfaces 119 and 121of the stratum 120, respectively. Further, the other holes are similarlysituated.

FIG. 2 shows a cut-away, exploded, isometric top view of retainingmechanism 200 of FIG. 1. As shown in FIG. 2, the stratum 120 is furtherconfigured to engage the retaining element 160. As shown in FIG. 2, thesecond surface 121 of the stratum 120 comprises a first recess 124configured to engage the retaining element 160. Further, as shown inFIG. 2, the first recess 124 comprises a second recess 126 configured toengage the spring element 130, and more specifically, to accommodatemovement of the spring element 130 when the retaining element 160 movesbetween its first and second positions. Yet further, as shown in FIG. 2,the first recess 124 further comprises a third recess 127 configured toengage the spring element 130, and more specifically, to maintainengagement between the spring element 130 and the stratum 120.

As shown in FIG. 2, the first recess 124 is situated in a plane that issubstantially parallel to the second surface 121 of the stratum 120.Further, the second surface 121 of the stratum 120 is substantiallyparallel to the first surface 119 of the stratum 120. As shown in FIG.2, the stratum 120 has a central hole 123 that extends between the firstrecess 124 and the second surface of the stratum 120, and that extendsin a direction substantially perpendicular to the first recess 124 andthe second surface of the stratum 120. As shown in FIG. 2, the centralhole 123 comprises a sidewall 125 and the second recess 126 extendsradially from the central hole 123, which is in a directionsubstantially parallel to the second surface 121. Further, as shown inFIG. 2, the third recess 127 extends from the second recess 126 and in aplane that is substantially parallel to the second surface 121.

In addition, as shown in FIG. 2, the retaining element 160 furthercomprises a first cut-out 164 and a second cut-out 166 on one end of theretaining element 160. On the opposite end of the retaining element 160,there is another pair of cut-outs (not marked) that are similar to thefirst and second cut-outs 164 and 166. In addition, as shown in FIG. 2,situated between the first and second cut-outs 164 and 166, there is afirst leg 163 of the retaining element 160. Further, as shown in FIG. 2,there is a second leg 165 on the opposite end of the retaining element160. Note that the first and second legs 163 and 165 of the retainingelement 160 are situated in a plane that is substantially parallel toeach of the first and second surfaces 119 and 121 of the stratum 120.

FIG. 3 shows a cut-away, isometric top view of the retaining mechanism200 of FIG. 1. As shown in FIG. 3, the retaining element 160 is in itsfirst position, which permits a fastener to be passed through the hole122 or 122A.

FIG. 4 shows a cut-away, isometric bottom view of the retainingmechanism 200 of FIG. 1. As shown in FIG. 4, the retaining element 160further comprises a grommet portion 169 situated between holes 122 and122A. The grommet portion 169 helps the retaining element 160 maintainposition affixed to the stratum 120, but also allows the retainingelement 160 to rotate, for example, between its first position and itssecond position.

FIG. 5 shows an isometric top view of the retaining element 160 ofFIG. 1. As shown in FIG. 5, a cam 170 or projection of material 170 isvisible in phantom lines (as well as in some other figures) because itis situated on the underside of the retaining element 160. Further, FIG.5 also shows the first leg 163 and the second leg 165 of the retainingelement 160. Note that the cam 170 extends and lies in a plane that issubstantially parallel to the legs 163 and 165 of the retaining element160.

FIG. 5A shows an isometric bottom view of the retaining element 160 ofFIG. 1. As shown in FIGS. 5 and 5A, the retaining element 160 furthercomprises a central shaft 167 that is configured to pass through thestratum 120. As shown in FIGS. 5 and 5A, at least the top of the centralshaft 167 has a hexagonal shape. Also, as shown, the central shaft 167defines a hole through the retaining element 160 and is situated at ornear the center of the retaining element 160. As shown, the retainingelement 160 may be rotated by, for example, inserting a hexagonal-shapedend of a tool into the central shaft 167 to thereby rotate the retainingelement 160 from, for example, its first position to its secondposition, or vice versa. Note that the central shaft 167 (andcorresponding tool) need not have a hexagonal-shape, but may be one of avariety of shapes so long as the function of rotating the retainingelement 160 can be accomplished. For example, other polygonal shapessuch as a square would suffice.

As shown in FIG. 5A, the central shaft 167 has a first portion 168 and asecond portion 169. The first portion 168 of the central shaft 167 isadjacent the grommet portion 169 and the first surface 119 (or bottom)of the stratum 120. The second portion 169 of the central shaft 167 isadjacent the second leg 165 of the retaining element 160 and the secondsurface 121 (or top) of the stratum 120. As shown in FIG. 5A, the cam170 of retaining element 160 is situated on and extends from the secondportion 169 of the central shaft 167. As shown in FIG. 5A, the cam 170is substantially triangular in shape or substantially beak-shapedprojection of material, i.e., projecting from the central shaft 167.

FIG. 6 shows a cut-away, isometric top view of the stratum 120 ofFIG. 1. FIG. 6 shows an enlarged view of the first recess 124, thesecond recess 126, the third recess 127 and the spring element 130. Asshown in FIG. 6, the third recess 127 has a first end 127 a and a secondend 127 b. Further, as shown in FIG. 6, the stratum 20 further comprisesa central hole 123 configured to receive the central shaft 167 of theretaining element 160. As shown in FIG. 6, the central hole 123 issituated in a plane that is substantially perpendicular to the plane inwhich the first recess 124 lies.

With reference to the figures, when the retaining element 160 isrotated, e.g., from the first position to the second position, the cam170 rotates and imparts a force against the spring element 130. The endsof the spring element 130 are held in position in the ends 127 a and 127b of the third recess 127 and when the cam 170 rotates and contacts thespring element 130, the spring element 130 flexes and moves into aportion of or all of the second recess 126. Note that the spring element130 moves in a direction substantially parallel to the second surface,and substantially parallel to the first recess 124, which also issubstantially perpendicular to the central hole 123 of the stratum 120.

As shown in FIG. 6, the second recess has an arcuate shape toaccommodate the spring element 130 when it is flexed by the cam 170.More specifically, when the retaining element 130 is in its firstposition to allow for insertion of fasteners through holes 122 and 122Aof the stratum 120, the cam 170 is situated closer to the first end 127a of the third recess 127 than the second end 127 b. The resting stateof the spring element 130 is that as shown in FIG. 6. Thus, when theretaining element 130 is in its first position, the spring element 130helps maintain the retaining element 130 in its first position. When asurgeon (or other person) wishes to prevent inadvertent backing out offasteners from the stratum 120, the retaining element 130 is rotatedapproximately ¼ turn (approximately 90 degrees) in the clockwisedirection and must overcome the force of the spring element 130.Similarly, when the retaining element 130 is in its second position, thecam 170 is situated closer to the second end 127 b of the third recessthan the first end 127 b and the spring element 130 helps maintain theretaining element 130 in its second position.

Note that the cam 170 need not be substantially triangular in shape orsubstantially beak-shaped but its shape may vary as long as the functionof maintaining the retaining element 130 in its first and secondpositions, and allowing movement between the two positions, isaccomplished. For example, a frusto-conical shape or more hemisphericalshape or other polygonal shape may work as well. Similarly, note thatthe second recess 126 need not have an arcuate shape, but may vary aslong as the function of allowing room for the spring element 130 to move(or flex) when the retaining element 130 moves between its firstposition and its second position is accomplished. For example, thesecond recess 126 may be more rectangular or some other polygonal shapemay work as well.

FIG. 7 shows a cut-away, isometric top view of the retaining mechanism200 of FIG. 1. Specifically, FIG. 7 shows an enlarged view of the areasurrounding the retaining element 160 when it is in its first position.As shown in FIG. 7, when the retaining element 160 is in its firstposition, the first cut-out 164 and the second cut-out 166 of theretaining element 160 permit first and second fasteners to be passedthrough the first and second holes 122 and 122A of the stratum 120,respectively. Further, as shown in FIG. 7, when the retaining element160 is in its first position, the cam 170 on the underside of theretaining element 160 engages the spring element 130. In this way, thecam 170 helps maintain the retaining element 160 in its first position.

FIG. 8 shows another cut-away, isometric top view of the retainingmechanism 200 of FIG. 1. Specifically, FIG. 8 shows an enlarged view ofthe area surrounding the retaining element 160 when it is in its secondposition. As shown in FIG. 8, a first fastener 40 and a second fastener40A has already been fully inserted into the first and second holes 122and 122A of the stratum 120, respectively. Further, as shown in FIG. 8,after the fasteners 40 and 40A have been fully inserted, the retainingelement 160 has been rotated in the clockwise direction approximately ¼turn from its position of FIG. 7. During rotation of the retainingelement 160, the cam 170 presses against the spring element 130 and thespring element 130 flexes, allowing the cam 170 and retaining element160 to rotate to its second position—as shown in FIG. 8. Note that whenthe spring element 130 flexes, the middle portion of the spring element(i.e., that portion not situated and held in place in the ends 127 a and127 b of the third recess 127) temporarily moves into the space providedby the second recess 126. As shown in FIG. 8, the when the retainingelement 160 is in its second position, the first leg 163 and the secondleg 165 of the retaining element 160 partially overlap the first andsecond holes 122 and 122A of the stratum 120, respectively, so as toprevent inadvertent backing out of fasteners 40 and 40A. Further, asshown in FIG. 8, when the retaining element 160 is in its secondposition, the cam 170 engages the spring element 130 so as to helpmaintain the retaining element 160 in its second position. When theretaining element 160 is in its second position, the spring element 130is less stressed than when the retaining element 160 rotates between itsfirst and second positions, but applies enough pressure against the cam170 to help maintain the retaining element 160 in its second position.

FIG. 9 shows an isometric top view of another embodiment of a retainingmechanism for affixing a stratum to bone. Specifically, FIG. 9 shows aretaining mechanism 300 for affixing a stratum 220 to a single level ofvertebrae, i.e., to connect two adjacent vertebral bodies. Bycomparison, the stratum 220 of FIG. 1 is used to connect three vertebralbodies (two levels of vertebrae). As shown in FIG. 9, the stratum 220has four holes, with each vertebral body receiving two fasteners, onefastener through each hole, for example, holes 222, 222A, 223 and 223A.Further, the retaining mechanism 300 comprises a retaining element 260,which has a different shape than retaining element 160.

FIG. 10 shows a top view of the retaining element 160 of FIG. 9. Asshown in FIG. 10, a cam 270 is visible in phantom lines because it issituated on the underside of the retaining element 260. Further, FIG. 10shows that retaining element 260 has four legs, where two legs arelarger than the other two legs. Specifically, legs 263 and 265 aresimilar in shape and they are larger than legs 234 and 266, whichthemselves are similar in shape. As with retaining mechanism element160, the cam 270 of retaining element 260 extends and lies in a planethat is substantially parallel to the legs 263, 265, 264 and 266.

FIG. 11 shows another top view of the retaining mechanism 300 of FIG. 9.Note, however, that FIG. 11 does not show the retaining element 260 anddoes not show a spring element (230 shown in FIGS. 12 and 12A). As shownin FIG. 11, the stratum 220 comprises a first recess 224, a secondrecess 226 and a third recess 227, all of which serve similar functionsas the recesses of the stratum 120 of retaining mechanism 200. Further,as shown in FIG. 11, the third recess 227 comprises ends 227 a and 227b, which are configured to engage the spring element 230, and morespecifically, to maintain engagement between the spring element 230 andthe stratum 220.

FIG. 12 shows a top view of a spring element such as 130 for use withretaining mechanism 200, or a spring element such as 230 for use withretaining mechanism 300. FIG. 12A shows a side view of the springelement 130, 230 of FIG. 12. As shown in FIGS. 12 and 12A, the springelements 130 and 230 each have a substantially cylindrical shape or thatof a rod having a circular cross section.

FIG. 13 shows a top view of another embodiment of a retaining mechanism400 for affixing a stratum to bone. Specifically, FIG. 13 shows aretaining mechanism 400 (retaining element 360 shown in FIG. 14) foraffixing a stratum 320 to a single level of vertebrae, i.e., to connecttwo adjacent vertebral bodies. As shown in FIG. 13, the stratum 320 hasonly two holes 322 and 322A, one hole 322 for one vertebral body and theother hole 322A for the adjacent vertebral body. Specifically, hole 322is configured to receive a fastener that engages with one vertebralbody, and hole 322A is configured to receive another fastener thatengages with an adjacent vertebral body.

As shown in FIG. 13, note that the figure does not show the retainingelement 360 and does not show a spring element. The spring elementintended to work with the retaining mechanism 400 would be similar infunction and shape to the spring element 230 shown in FIGS. 12 and 12A.As shown in FIG. 13, the stratum 320 comprises a first recess 324, asecond recess 326 and a third recess 327, all of which serve similarfunctions as the recesses of the stratum 120 of retaining mechanism 200.Further, as shown in FIG. 13, the third recess 327 comprises ends 327 aand 327 b, which are configured to engage the spring element, and morespecifically, to maintain engagement between the spring element and thestratum 320. Note that stratum 320 need not be limited to connected twoadjacent vertebrae, but may be designed to connect more than twovertebrae such that each level of vertebrae would have a single hole forreceiving a single fastener.

FIG. 14 shows a top view of the retaining element 360 to be used withthe retaining mechanism 400 of FIG. 13. Specifically, the retainingelement 360 is configured to be positioned in the first recess 324. Asshown in FIG. 14, a cam 370 is visible in phantom lines because it issituated on the underside of the retaining element 360. Further, FIG. 14shows that retaining element 360 has two legs 363 and 365. Specifically,situated between legs 263 and 265 are cut outs 364 and 366. As withretaining mechanism element 160, the cam 370 of retaining element 260extends and lies in a plane that is substantially parallel to the legs363 and 365.

Parts of the retaining mechanisms 200, 300 and/or 400 may have a varietyof shapes and sizes and still accomplish the functions described herein.For example, the shape of the retaining elements 160, 260 and/or 360 orany of its constituent parts may be different than that shown in theFigures as long as they accomplish their respective functions describedherein. The retaining elements 160, 260 and/or 360 may be any shape aslong as it allows for insertion of fasteners and helps preventinadvertent backing out of the fasteners after the fasteners have beenfully inserted into the holes (for example, hole 122 or 122A).

In the embodiments shown and described herein, the retaining elements160, 260 and/or 360 are substantially rigid. Further, in the embodimentsshown and described herein, each stratum 120 (or 220 or 320) issubstantially rigid. Accordingly, the recesses 124, 126 and 127 (or 224,226 and 227, or 324, 326 and 327) therein are substantially rigid.

The term “substantially” as used herein may be applied to modify anyquantitative representation which could permissibly vary withoutresulting in a change in the basic function to which it is related. Forexample, the retaining element 160 may be considered substantially rigidif when the retaining element 160 is in its second position, theretaining element 160 at least partially overlaps a hole 122 or 122A soas to help prevent inadvertent backing out of a fastener after thefastener has been fully inserted into the hole.

In the embodiments described herein, a stratum may be made of a varietyof biocompatible materials (metal or non-metal), including but notlimited to, Titanium Alloys, commercially available Titanium, stainlesssteel, polyetheretherketone (“PEEK”), cobalt chrome (“CoCr”),polyetherketoneketone (“PEKK”), ultra high molecular weight polyethylene(“UHMWPE”), polyethylene, shape memory metals, other polymers or anycombination of such materials. Similarly, the retaining mechanisms 160,260 and 360 and/or the fasteners (for example, fastener 40) may be madeof the same materials. Also, any suitable materials know in the art maywork for each of these elements as well as for other elements describedherein.

In the embodiments shown, the spring elements 130, 230 (or that usedwith retaining mechanism 400) have elastic properties. Thus, each springelement 130, 230 comprises a material that has elastic properties. Forexample, each spring element 130, 230 may comprise a material such asmetal that is elastic. In addition, each spring element 130, 230 (asexamples) may be made of Nickel Titanium (NiTi), commercially pureTitanium, a Titanium alloy or any combination of such materials.Further, as noted, the spring elements 130, 260 may have shapes otherthan substantially cylindrical. That is, the spring elements 130, 260may take any form that satisfies its function described herein, forexample, being able to adequately engage with the retaining elements 160(or 260) and the stratum 120 (or 220) and being able to sufficientlymaintain the retaining element 160 (or 260) in its second position so asto not allow the fasteners (for example, fastener 40) to inadvertentlyback out of the stratum 120 (or 220). For example, although the springelement 130 (or 230) is shown as having a substantially cylindricalshape or that of a rod having a circular cross section, a variety ofshapes may be employed. For example, a rod or member having a morerectangular or cross section of a square may work as well.

All adjustments and alternatives described above are intended to beincluded within the scope of the invention, as defined exclusively inthe following claims. Those skilled in the art also should realize thatsuch modifications and equivalent constructions or methods do not departfrom the spirit and scope of the present disclosure, and that they maymake various changes, substitutions, and alterations herein withoutdeparting from the spirit and scope of the present disclosure.Furthermore, as used herein, the terms components and modules may beinterchanged. It is understood that all spatial references, such as“superior,” “inferior,” “anterior,” “posterior,” “outer,” “inner,”“upper,” “underside,” “top,” “bottom,” and “perimeter” are forillustrative purposes only and can be varied within the scope of thedisclosure.

The invention claimed is:
 1. A retaining mechanism comprising: a stratumcomprising a first surface and an opposite second surface, the stratumcomprising a hole extending through the first and second surfaces; aretaining element comprising a body including a cutout, the retainingelement being rotatable between a first position in which the cutout isaligned with the hole to permit a fastener to be passed through the holeand a second position in which the body at least partially overlaps thehole; and a spring element positioned between the stratum and theretaining element, the spring element being configured to engage theretaining element to help maintain the retaining element in the firstposition and the second position.
 2. A retaining mechanism as recited inclaim 1, wherein the spring element is less stressed when the retainingelement is in the second position than when the retaining element movesbetween the first and second positions.
 3. A retaining mechanism asrecited in claim 2, wherein the spring element applies pressure againstthe retaining element when the retaining element is in the secondposition.
 4. A retaining mechanism as recited in claim 1, wherein theretaining element rotates about an axis that extends substantiallyperpendicular to the first and second surfaces to move the retainingelement between the first and second positions.
 5. A retaining mechanismas recited in claim 4, wherein the spring moves in a direction that issubstantially parallel to the first and second surfaces as the retainingelement moves between the first and second positions.
 6. A retainingmechanism as recited in claim 1, wherein the spring element is in aresting state when the retaining element is in the first position,wherein the spring element is linear when in the resting state.
 7. Aretaining mechanism comprising: a stratum comprising a first surface andan opposite second surface, the stratum comprising a first hole and asecond hole that is spaced apart from the first hole, the first andsecond holes each extending through the first and second surfaces; aretaining element comprising a body including a first cutout and asecond cutout that is spaced apart from the first cutout, the retainingelement comprising a first position in which the first cutout is alignedwith the first hole and the second cutout is aligned with the secondhole to permit a fastener to be passed through each of the first andsecond holes and a second position in which the body at least partiallyoverlaps the first hole and the second hole; and a spring elementpositioned between the stratum and the retaining element, the springelement being configured to engage the retaining element to helpmaintain the retaining element in the first position and the secondposition, wherein the stratum comprises a third hole situated betweenthe first and second holes, the third hole extending through the firstand second surfaces, a portion the retaining element being rotatablypositioned within the third hole.
 8. A retaining mechanism as recited inclaim 7, wherein the spring element is less stressed when the retainingelement is in the second position than when the retaining element movesbetween the first and second positions.
 9. A retaining mechanism asrecited in claim 8, wherein the spring element applies pressure againstthe retaining element when the retaining element is in the secondposition.
 10. A retaining mechanism as recited in claim 7, wherein theretaining element rotates about an axis that extends substantiallyperpendicular to the first and second surfaces to move the retainingelement between the first and second positions.
 11. A retainingmechanism as recited in claim 7, wherein the stratum comprises a thirdhole situated between the first and second holes, the third holeextending through the first and second surfaces, the third hole having agrommet disposed therein, the retaining element engaging the grommet torotate the retaining portion about an axis that extends substantiallyperpendicular to the first and second surfaces.
 12. A retainingmechanism as recited in claim 7, wherein the stratum comprises a thirdhole situated between the first and second holes, a shaft of theretaining element being rotatably positioned within the third hole, theshaft extending from a body of the retaining element.
 13. A retainingmechanism as recited in claim 12, wherein the stratum comprises a firstrecess defined by a third surface of the stratum, the third surfacebeing substantially parallel with the first and second surfaces andpositioned between the first and second surfaces, wherein a bottomsurface of the body engages the third surface, the bottom surface beingpositioned between a top surface of the body and the shaft.
 14. Aretaining mechanism as recited in claim 13, wherein the stratumcomprises second and third recesses that are in communication with thefirst recess and the third hole, the spring element being positionedwithin the first recess when the retaining element is in the firstposition and the spring element extending into the second recess whenthe retaining element is in the second position.
 15. A retainingmechanism as recited in claim 14, wherein the third recess extends fromthe second recess in a plane that is substantially parallel to thesecond surface.
 16. A retaining mechanism as recited in claim 13,wherein opposite first and second end surfaces of the spring element arepositioned within first recess when the retaining element is in thesecond position.
 17. A retaining mechanism as recited in claim 7,wherein the spring element is in a resting state when the retainingelement is in the first position, wherein the spring element is linearwhen in the resting state.
 18. A retaining mechanism as recited in claim7, wherein the spring moves in a direction that is substantiallyparallel to the first and second surfaces as the retaining element movesbetween the first and second positions.
 19. A retaining mechanism asrecited in claim 7, wherein opposite ends of the stratum each comprise arecess configured for disposal of an insertion instrument.
 20. Aretaining mechanism comprising: a stratum comprising a first surface andan opposite second surface, the stratum comprising a hole extendingthrough the first and second surfaces; a retaining element comprising abody including a cutout, the retaining element comprising a firstposition in which the cutout is aligned with the hole to permit afastener to be passed through the hole and a second position in whichthe body at least partially overlaps the hole; and a spring elementpositioned between the stratum and the retaining element, the springelement being configured to engage the retaining element to helpmaintain the retaining element in the first position and the secondposition, wherein the spring element is in a resting state when theretaining element is in the first position, and wherein the springelement is linear when in the resting state.